When one sex carries the other during some phase of courtship or mating, the associated loading may entail a significant cost to the carrier. This paper presents a series of laboratory experiments designed to identify the costs of mate-carrying in Aquarius remigis. Female A. remigis mate repeatedly and carry each mate for several hours. Dead males and lead weights were used to simulate normal mating and loading associated with mate-carrying, respectively. Females carrying weights equivalent to the weight of an average male showed no detectable reductions in survival, lipid reserves, or foraging success, and maintained themselves on the water surface for more than 10 days without access to resting sites. Weights equivalent to two males were supported for 6.1 ± 4.9 days. Thus, female A. remigis appear to be very well adapted to carrying their mates and are unlikely to be near their load limits when carrying a single mate. However, females carrying males or equivalent weights suffered a significant reduction in maximum mobility (stride length and speed), and an increased risk of predation by frogs (Rana clamitans). Females carrying weights were more susceptible to predation than unburdened females but were less susceptible than females carrying males, suggesting that loading contributes significantly to, but does not fully explain, the increased predation risk. This risk probably results from both reduced mobility due to loading and greater visibility (size). Possible influences of the costs of loading on mating behavior and sexual size dimorphism are discussed.

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